In Ref. [1]}, Schomerus compared the resistances of NGN
junctions and GGG structures, and found the duality between
graphitic and normal-conduncting contacts. He has shown that
identical transport properties arise when the graphitic leads are
replaced by quantum wires and the difference between the results
obtained in those structures is only quantitative. On this basis, we
plot in Fig. 4(a) the conductance as a function of \(U_G\)  in the NGN
junction in comparison with the GGG structure for the case of \(L_D =51\)  nm and \(E_F = 300\)  meV. Since we found that the results depend
weakly on the hopping energy in the leads, \(t_L\)  is chosen to be
equal to \(t\)  for simplicity. Qualitatively, Fig. 4(a) shows that the
oscillation of conductance seem to be unchanged in its phase and
period when changing the leads. Quantitatively, the oscillation in
the NGN junction is stronger than in the GGG structure. This can be
explained clearly by the effect of replacing the graphitic leads by
the normal conducting ones on the picture of bound states in the
barrier region. These states, in the framework of the Dirac's
description, have been considered as confined hole states in the
\(2D\) -graphene structures [2]}. In Fig. 4(b), we display the
LDOS (see the right axis for graphitic and the left axis for
normal-conducting leads) at the first site of barrier region with
respect to \(U_G\) . The results are understood that the peaks of LDOS
occur when the Fermi energy corresponds to any bound state.
Obviously, the oscillation of LDOS (or the quantization of bound
states in the barrier) in the NGN junction appears stronger (with
higher peaks) than that in the GGG structure. It is the essential
origin of the different behaviors of conductance as shown in Fig.
4(a).
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